1. Field of the Invention
This invention relates to a method of improving the heat stability of pigmentable silicone elastomers that are catalyzed with organic peroxides and vulcanized with heat.
2. Description of the Prior Art
Elastomeric materials based upon polyorganosiloxane polymers have found usefulness in part due to the resistance of the materials to the effects of elevated temperatures. In spite of the inherent heat stability of the polyorganosiloxane polymers, much work has been done to improve their heat stability.
The majority of the heat stability additives discovered are metallic oxides. Iron oxide is the most commonly used metallic oxide. Some metallic salts are also useful. Many of these additives are not useful when it is desired to impart a particular color to the elastomer, because the metallic oxides and salts, per se, produce color in a silicone elastomer.
In U.S. Pat. No. 3,341,489, issued Sept. 12, 1967, Simpson discloses the addition of certain olefinically unsaturated organosilicon materials such as vinyltriethoxysilane to an organopolysiloxane composition which is convertible to a cured, solid, elastic state. The resulting composition could be directly fabricated to valuable elastomeric products without the necessity of an extended post-cure.
A great variety of different types of materials have been taught as being useful fillers in silicone elastomers ranging from carbon black through finely ground metallic oxides such as silica and aluminum oxide to colloidal silica. Naturally occuring filler materials such as diatomaceous earth and clay have been used.
A brochure entitled "Silane Coupling Agents in Mineral-Reinforced Elastomers", published by Union Carbide Corporation, marked F-44715B, suggests that fillers such as calcined clays treated with vinyl functional silanes can be added to mineral-filled peroxide-cured elastomers, including silicone elastomers, to improve the mechanical and dynamic properties of elastomers. There is no teaching as to a method of improving the heat stability of silicone elastomers. Such treated inorganic fillers have been used in polyester resins, crosslinked polyethylene, ethylene-propylene rubber, and ethylene-propylene terpolymers to give products having improved physical properties.